1. Field of the Invention
The present invention relates to a method and apparatus for inspecting an extruded tread and, particularly, to a method and apparatus for checking the internal structure of an extruded tread on an on-line basis.
2. Description of the Prior Art
FIG. 4 is a diagram showing the outline of a tread extrusion step in which a rubber material produced in an unshown rubber kneading step is shaped like a belt by a warmer 51, supplied to an extrusion molding machine 52 to be molded to have a predetermined cross section, cooled in a cooling water tank 53 and cut to a length corresponding to one tire by a cutting machine 54 such as a tread skiver. The above cut extruded tread 20 is placed on a belt conveyor 55 as conveying means, carried on a tread carrier to a molding step and laminated with another member such as a cord, bead or belt on the molding machine to be assembled into one crude tire. In the figure, a molding machine for molding a single rubber material is illustrated to make the figure simple. A multilayer extruder for extruding different kinds of rubber at the same time is widely used as the extrusion molding machine. To cut the rubber material, the belt-like tread may be wound up by a winder and then cut when it is wound a required length.
After cutting, the outer shape, length, width and the like of the above extruded tread 20 and further the mass thereof are measured to check its quality for screening. These measurements are generally carried out on all the treads on an on-line basis.
The above extruded tread 20 consists of a plurality of rubber layers which differ from one another in composition. A material having excellent durability and abrasion resistance is used in a cap tread portion which is in contact with a road and a material having excellent adhesion to a cord, a small difference in stiffness from that of the cord and high hardness is used in a base tread portion which is in contact with the cord on the inner side. For the inspection of the tread, the cross section of the tread is observed and whether the internal structure of the extruded tread 20, that is, the lamination state of the rubber layers is good is judged from differences in gloss among rubber layers caused by use of different materials in the laminated rubber layers.
However, the above inspection is carried out by cutting a trial sample manufactured for an extrusion test prior to the actual production or a sample extracted from a production lot of actually extruded products and measuring the sample with the eye or loupe on an on-line base. Therefore, the production line cannot be re-started until the inspection result of the above internal structure is obtained, thereby reducing production efficiency.
To judge the internal structure by visual inspection accurately and quickly, an operator needs some skill. Therefore, it has been desired to simplify and increase the efficiency of the above inspection.
It is an object of the present invention which has been made in view of the problems of the prior art to provide a method and apparatus capable of checking the internal structure of an extruded tread efficiently and accurately.
According to a first aspect of the present invention, there is provided a method of inspecting an extruded tread, comprising the steps of:
photographing the cut section of an extruded tread;
processing the obtained image; and
locating the boundaries among rubber layers on the above cut section from differences in brightness among the rubber layers which differ in composition.
This makes it possible to easily and accurately identify the boundaries among the rubber layers and to inspect the internal structure of the extruded tread without extracting an inspection sample from the production lot, whereby the inspection can be simplified and the efficiency of the inspection can be improved.
According to a second aspect of the present invention, there is provided an apparatus for inspecting an extruded tread, comprising:
means of photographing the cut section of an extruded tread, the means being installed near a line for conveying the extruded tread after cutting;
means of processing an image of the photographed cut section of the extruded tread to locate the boundaries among rubber layers which differ in composition on the cut section from differences in brightness among the rubber layers of the image; and
means of judging whether the internal structure of the extruded tread is satisfactory or not by comparing the above located boundaries with preset reference boundaries.
Thus, the apparatus can check the internal structure of the extruded tread without extracting an inspection sample from the production lot.
According to a third aspect of the present invention, there is provided an apparatus for inspecting an extruded tread which further comprises means of illuminating a site to be photographed of the cut section at a predetermined angle in order to more clearly photograph differences in the gloss of the cut section.
The above and other objects, features and advantages of the present invention will become apparent from the following description taken into connection with the following drawings.